Over the years, the audio industry has introduced new technologies that have steadily improved the realism of reproduced sounds. The 1940's monaural high fidelity technology led to the 1950's stereo. In the 1980's, digitally based stereo was introduced to improved the realism of reproduced sounds. Recently, spatial enhanced sound systems have come into existence. These systems give the listener a 180 degree, planner two dimensional presentation of sound. Listeners perceive a "widened" or "broadened" soundstage where sounds apparently are not limited to the space between the two speakers as in a conventional stereo system. Although offering more depth than conventional stereo systems, it falls short of providing full and realistic three-dimensional sounds.
Positional three-dimensional sound systems recreate all of the audio cues associated with a real world, and sometimes surrealworld, audio environment. The big difference between spatial enhanced and positional three-dimensional sound is that spatial sound uses two tracks and must evenly apply signal processing to all sounds on the track. Positional three-dimensional audio processes individual sounds according to Head Related Transfer Function (HRTF) techniques and then mixes the processed individual sounds back together before final amplification. This enables imbuing individual sounds with sufficient spatial cuing information to present an accurate, convincing rendering of an audio soundscape just as one would hear it in real life.
In a typical sampling arrangement, sound is typically sampled at a plurality of different rates ranging from 48 kHz all the way down to 5 kHz (sound is typically stored at 48, 44.1, 22.05, 11.025, and 5.6125 kHz). The reason for having the different sampling rates is that programmers are trying to save as much memory space as possible. Programmers do not want to use all the memory space on sound.
The main problem with sampling is that the corresponding maximum frequency that may be reproduced is approximately 20,000, 10,000, 5,000, and 2,500 respectively. This is due to the fact that under sampling theory, one can reproduce a frequency which is less than half the sampled frequency. Thus, even though most sounds contain some high frequency components, frequencies above the maximum are eliminated before sampling. The result is that sounds stored at lower sampled rates do not lend themselves very well to three dimensional audio positioning. As an example, if a sound has few high frequency components, the sound will be filtered to eliminate the high frequencies and then sampled at the lowest rate possible to conserve sample size. The sampled sound will then be converted up and positioned. The problem is that the sound will only have the low frequency components to position. Therefore, the listener will only receive a small percentage of the cues required to properly position the sound.
Therefore, a need existed to provide a method of improving three-dimensional sounds for all listeners. The method will allow higher frequency harmonics to be added into sampled sounds thereby creating a replica of the high frequency sound components that were eliminated prior to sampling. The method will provide a resulting frequency spectrum containing a larger number of frequencies that may be manipulated to allow for more realistic three dimensional audio positioning.